Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $87.61   13.661%   $99.5784   $99.58   $99.60   $99.60  
  Purchase #2 $139.81   4.569%   $146.1979   $146.20   $146.20   $146.20  
  Purchase #3 $61.91   3.601%   $64.1394   $64.14   $64.15   $64.10  
  Purchase #4 $180.70   13.123%   $204.4133   $204.41   $204.40   $204.40  
  Purchase #5 $108.73   10.837%   $120.5131   $120.51   $120.50   $120.50  
  Purchase #6 $175.70   3.762%   $182.3098   $182.31   $182.30   $182.30  
  Purchase #7 $203.44   12.494%   $228.8578   $228.86   $228.85   $228.90  
  7 purchase totals = $957.90       $1,046.0097   $1,046.01   $1,046.00   $1,046.00